Internet Engineering Task Force (IETF) is an organization which sets standards of Internet-related technologies. The IETF formally issues documents to lay open various technologies. One of them is functional enhancement of a routing technique using Multi-Protocol Label Switching (MPLS), which is a packet-transfer technique based on label switching (see “RFC 3606”, [online], Internet <http://www.ietf.org/rfc/rfc4202.txt> searched on Jun. 22, 2007; “RFC 4202”, [online], Internet <http://www.ietf.org/rfc/rfc3606. txt> searched on Jun. 22, 2007; and “draft-ietf-ccamp-gmpls-routing-ospf-02”, [online], Internet <http://rfc.netvolante.jp/internet-drafts/draft-ietf-ccamp-gmpls-ason-routing-ospf-02.txt> searched on Jun. 22, 2007).
MPLS performs distribution and collection of link information (topology information) that indicates a network connection status used by a label switch network according to Open Shortest Path First (OSPF), and collects link connection information between nodes in the network.
Specifically, each node advertises information about a link whose starting point is the own node. Each node exchanges the information about the link with each of the other nodes, thereby transmitting link information to all nodes in the network. As a result, the all nodes in the network grasp link connection information among the all nodes in the network.
For example, a representative routing controller (hereinafter, “representative RC”) that transmits and receives link information is provided in each routing area in a hierarchical network including leveled routing areas. When receiving link information through feed-up of transmitting link information from a lower level to an upper level, or feed-down of transmitting link information from an upper level to a lower level, the representative RC advertises the received link information to another RC in a routing area on the same routing level. In this way, each node in each routing area grasps link information of the entire network.
However, the conventional technology described above has a problem that there is a time during which link information is not advertised, and consistency of the link information may not be maintained. Specifically, when a representative RC stalls its function due to a failure, a Link-State Advertisement (link LSA) that is held by the representative RC and indicates an advertiser and a link connection status remains in its routing area, and a representative RC in charge of feed-up or feed-down is not replaced, resulting in an absence of such representative RC in the routing area, and link information is not advertised for a certain period of time.